Mutations in COL4A3, COL4A4, or COL4A5—encoding the α3, α4, or α5 (IV) chains, respectively—cause various diseases, including thin basement membrane nephropathy (TBMN), Alport syndrome (AS), and late-onset focal segmental glomerulosclerosis (FSGS) [2]. Here, COL4A4 is linked to focal segmental glomerulosclerosis.